This invention relates to a light radiating device for radiating light against a heatsensitive stencil sheet overlapped on an original image in a heatsensitive perforating device in which an image is perforated in heatsensitive manner on the heatsensitive stencil sheet.
FIG. 6 is a perspective view for showing the prior art heatsensitive perforating device 1 which was proposed by the inventor of the invention. In this figure, a pressing plate 3 is pivotally attached to a base 2. On the upper surface of the base 2 is arranged a base-seat 4 on which an original is mounted. The lower surface of the pressing plate 3 opposing against the base-seat 4 is provided with an opening 6 having a transparent plate 5 therein. At the lower surface side of the transparent plate 5 is removably installed an assembly of the heatsensitive stencil sheet. The assembly of a heatsensitive stencil sheet is made such that the heatsensitive stencil sheet made of a porous supporting member and a heatsensitive film adhered to the supporting member is fixed to one surface of a frame and one side edge of an ink impermeable sheet is adhered to the other side of the frame.
As shown in FIG. 6, a light radiating device 10 is removably installed at the opening 6 of the pressing plate 3. The light radiating device 10 has an virtually quadrate pyramid casing 11. As shown in FIG. 7, a reflection mirror 22 is provided along the inner surface of the casing 11 (21) of the light radiating device 10. The reflection mirror 22 is comprised of lower side reflection mirrors 24 which contact with a perforating plane of the heatsensitive stencil sheet; an upper reflection mirror 23 which is parallel with the perforating plane of the heatsensitive stencil sheet and arranged in the same plane as that of the base of flash bulbs 12; and upper side reflection mirrors 25 which is arranged continuous with the lower side reflection mirrors 24 in a predetermined angle. The upper reflection mirror 23, the lower side reflection mirrors 24 and the upper side reflection mirrors 25 are all plane mirrors.
There is provided on the upper reflection mirror 23 with a hole 23a for being inserted by the flash bulbs 12. Plate spring-like electrode 26 is provided between the upper reflection mirror 23 and the casing 11.
An original is placed on the base-seat 4 of the base 2, the heatsensitive stencil sheet assembly is installed on the transparent plate 5 of the pressing plate 3 and then the light radiating device 10 is installed at the opening 6 of the pressing plate 3. As the pressing plate 3 is pressed against the base 2, the heatsensitive stencil sheet of the heatsensitive stencil sheet assembly is closely contacted with the original, so that a switch mechanism not shown in the figure is concurrently closed to cause the light radiating device 10 to be operated. The flash bulbs 12 may generate flash light and this flash light passes through the transparent plate 5 and the heatsensitive stencil sheet to cause an image in the original to be heated. A heatsensitive film of the heatsensitive stencil sheet is formed with perforated images corresponding to the image in the original.
This heatsensitive perforating device 1 is utilized as a printing device after perforating the sheet. That is, the ink impermeable sheet of the assembly is opened, ink is placed on the heatsensitive stencil sheet within the frame and again the ink impermeable sheet is closed. This assembly of the heatsensitive stencil sheet is installed at the pressing plate 3 with the heatsensitive stencil sheet being faced down. If a printing sheet is placed on the base-seat 4 of the base 2 and the pressing plate 3 is pressed against the base 2, the heatsensitive stencil sheet of the assembly is pushed against the printing sheet and then a screen printing is applied to the printing sheet.
In the perforating process performed in the aforesaid heatsensitive perforating device 1 of the prior art, the flash light for thermally perforating the heatsensitive stencil sheet is radiated in a substantial radial direction from the flash bulbs 12.
In the case where thermal perforation is performed with the light radiating device 10 of said heatsensitive perforating device 1, an operator attaches flash bulbs 12 to the light radiating device 10 by hand. Owing to degree of the manual power of the operator, the flash bulbs 12 are sometimes fixed in a leaning position unlike a regular one.
In this state, the bottom of the base portion does not certainly contact with the plate spring-like electrode 26, which sometimes causes perforation failure.
This light radiating device 10 has two flash bulbs 12,12. These two bulbs are positioned symmetrically relative to an imaginary center line of the stencil sheet and they are capable of radiating light equally to the stencil sheet; however, in the case where either one of the bulbs leans, they are not capable of radiating light equally to the stencil sheet, thereby causing perforating failure.
This undesirable phenomenon tends to happen prominently in the case where an image is formed approximately over an entire surface of the perforating plane or in the case that a solid print image is present at the outer circumference of the perforating plane.